Digital cameras and optical imaging devices employ image sensors. Image sensors convert optical images to digital data that may be represented as digital images. Image sensors include an array of pixels, which are unit devices for the conversion of an optical image into digital data. The pixels often manifest themselves as charge-coupled devices (CCDs) or complementary metal oxide semiconductor (CMOS) devices.
CMOS image sensors (CISs) have recently received more attention than CCD image sensors. CISs provide lower power consumption, smaller size, and faster data processing than CCD image sensors. Further, CISs provide a direct digital output of data that is not available in CCD image sensors. Even more, CISs have a lower manufacturing cost compared with CCD image sensors, since many standard semiconductor manufacturing processes may be employed to manufacture CISs. For these reasons, commercial employment of CISs has been steadily increasing in recent years.